Practical, clinical procedures will be developed for estimating optimum frequency-gain characteristics for both monaural and binaural hearing aids. A wearable master hearing aid, characterized by flexibility of response characteristics, will be used to precisely control frequency-gain characteristics. Part I of the study will be concerned with development and evaluation of a clinical procedure for fitting monaural hearing aids. Each initial estimate of the optimum frequency-gain characteristics is to be made on the basis of individual psychoacoustic data. The initial estimate will serve as starting point for a procedure involving a 3 x 3 factorial design which will include testing in a systematic manner at frequency-gain curves about the initial estimated optimum point. The object of Part II of the study is to develop an experimental protocol for determining optimum or near optimum frequency-gain characteristics for binaural amplification. The protocol will be an extension of that used in Part I, adding the factor of aided-ear (right vs. left) to the fixed design and using an adaptive procedure to further converage on the best estimate of the optimum.